Recording head for facsimile reproduction and the like



Oct. 21, 1952 c. w. JACOB 2,614,901

RECORDING HEAD FOR FACSIMILE REPRODUCTION AND THE LIKE Filed Aug. 4, 1949 2 SHEETS-SHEET l 30 28 I lg E L- 2.

w24 Pff i R. CARLYLE W JAGUB ATTORNEY Oct. 2l, 1952 c. w. JACOB RECORDING HEAD FO FACSIMILE REPRODUCTION AND THE LIKE Filed Aug. 4, 1949 2 SHEETS-SHEET 2 50 /lso www ATTORNEY JNVENTOR. CARLYLE W JACOB Patented Oct. 21, 1952 UNITED STATES PATENT ori-'ics RECORDING HEAD FOR FACSIMILE REPRODUCTION AND THE LIKE Carlyle W. Jacob, Rochester, N. Y.

Application August 4, 1949, Serial No. 108,553

26 Claims. l

The present invention relates t recording apparatus suitable for use in reproducing pictures or in making facsimiles of pictures, writings, maps, sketches, drawings, etc. More particularly the invention relates to apparatus in which a record is made upon a record-receiving medium through electronic control of one or more electrically charged streams or jets of air or gas containing ink or other marking particles by means of signals generated by scanning an original subject-matter sheet. In a still more specific aspect, the invention relates to an improvement on the electronic signal recording apparatus of my prior U. S. patent applications, Serial No. 2,624, filed January 16, 1948, and Serial No. 17,773, led March 29, 1948, which have resulted, respectively, in Patent No. 2,577,894, dated December 11, 1951, and Patent No. 2,573,143, dated October 30, 1951.

In the system and apparatus of my prior applications above mentioned, a marking liquid, such as ink, is atomized and directed through a duct vin a recording head or gun, the marking particles are charged with positive or negative ions by passing them through a corona discharge; and the stream of ionized particles are then passed through a duct in a precipitating unit in which an electrical eld is created, the intensity of which is controlled in accordance ywith received signals generated by scanning the subject-matter sheet. The electrical eld created in the precipitating unit will cause the charge particles to be precipitated on one side of the passageway through this unit. The percentage of particles deflected from the stream will depend on the magnitude of the signal. nal, the greater the number precipitated. A recording medium travels past the mouth of the precipitating duct. Since the number of droplets, that are deflected from the stream, is a function of the applied signals, the amount of ink deposited on the recording medium can be controlled from the applied signals. When the signal is at a maximum, all of the ink particles are precipitated from the stream, and consequently no mark will be produced on the recording medium. 4

In the recording heads or guns of my prior applications above mentioned, corona* rods or electrodes are used as the charging means; and only one charge is applied to the marking stream as it passes through the charging duct.

It has been found that when the gun is in operation stray mist particles sometimes accumulate on the corona rods or electrodes, causing an erratic corona discharge.

The greater the sig` It has been found very diiiicult also, to smoothly charge the particles of the mist stream to 'a maximum by one application of ions from one corona rod or electrode. The ions in flowing from the corona rod or electrode across the stream of mist produce a certain degree of eddying and turbulence in the mist. vIf the ion current is too heavy or the slot in the corona chamber is too Wide, the eddying will be so severe as to give the marking particles a large random momentum and cause them t0 impinge on the walls of the charging duct. This not `only removes particles from the stream but removes them unevenly. The concentration of particles in the mist will vary from volume to volume and cause the recording of the recording medium to appear mottled.

A primary purpose of the presentk invention is toprovide recording apparatus to the lcharacter described which will be more efficient in operation.

Another object of the invention is to provide recording apparatus of the character described which can .be kept continuously efficient.

Another object of the invention isito provide recording apparatus of the character described which will require less attention and remain in working order almost indeiinitely. l

A further object of the invention is to provide in a recording head or gun of the character described a corona electrode whose efficiency can be kept always at the desired level. v

Another object of the invention is'to provide a recording head or gun of the character de' scribed in which the mist stream may be charged in such a way as it travels through the recording head, as to avoid eddying and turbulence in the mist and prevent impinging of -marking particles on the walls of the charging duct.

A still further object of the invention is to provide a recording head or gun of the character described 'in which the mist stream may be charged a plurality of times as it passes through the charging duct, thereby to obtain the -mai i mum charge and increase the sensitivity of the charged particlesto the applied signals.

Still another object of the invention is to provide an apparatus of the character described in which provision is made for cleaning the charging electrodes and the ducts through which the streams of marking particles pass so as to prevent the marking particles from interfering with the efficiency of operation ofthe apparatus.

Other objects of the invention will be apparent 3 hereinafter from the specification and from the recital of the appended claims.

In the drawings:

Fig. 1 is a somewhat diagrammatic view showing in plan recording apparatus built according to one embodiment of this invention;

Fig. 2 is a section on the line 2-2 of Fig. l;

Fig. 3 is a vertical sectional view on an enlarged scale showing a single jet recording head built according to one embodiment of this invention in registry with the recording cylinder or drum;

Fig. el is a sectional view on the line 4 4 of Fig. 3 looking in the direction of the arrows;

Fig. 5 is a sectional view, similar to Fig. 3, but showing a different embodiment of recording head or gun;

Fig. 6 is a fragmentary vertical sectional view, similar to the views of Figs. 3 and 5, but showing a still further embodiment of the invention;

Fig. 7 is a fragmentary view in plan, similar to Fig. 4, but showing diierent means for cleaning the corona wire;

Fig. 8 is a vertical sectional view similar to the views of Figs. 3, 5, and 6 showing an embodiment of the invention in which means is provided in the recording ead or gun for supplying cleaning iluid to clean off the marking particles;

Fig. 9 is a fragmentary sectional View on the line Q -Ei of Fig. 8, looking in the direction of the Fig. l0 is a fragmentary vertical sectional view showing still another way in which cleaning iiuid may be applied to the corona chambers to clean away marking particles that may possibly have gotten therein.

Referring now to the drawings by numerals of reference, Figs. l and 2 show the recording apparatus generally.y This apparatus comprises a rotatable recording cylinder or drum'2 and a recording head El. The recording cylinder or drum has wrapped therearound a record-receiving or recording sheet 22. The recording cylinder or drum is suitably supported on a shaft 23 which is driven through suitable gearing 24 from a motor In the embodiment shown, the recording head 2l is mounted to move axially of the recording drum 2G as the latter rotates so that each elemental area or the recording receiving sheet 22 is scanned or explored by the recording head. The recording head is guided in its movement relative to the drum by guide-rods 26 and is moved by a lead screw 2l which may be driven from the motor 25 at the desired rate through gearing in the gear box 28. The above described elements of the recorder are suitably supported and attached to the base.

The recorder may be controlled by electrical signals derived in the same manner as are the recorders of my earlier applications, for instance, from a photocell scanner in which the picture to be reproduced is mounted on a synchronously driven drum as well known in the facsimile art.

The present invention relates to features of the recording head. Several different types of rec- Ording heads are disclosed in the drawings. All of these recording heads consist primarily of means whereby ink or other marking substances, such as etching acids, are sprayed or directed onto the record-receiving medium in accordance with and under the control of the applied signals.

The recording head shown in Figs. 3 and e, comprises a body whose upper portion is formed of a suitable metal and whose lower portion 35 is made of asuitable-insulating material such as a porous ceramic cr plastic. The con fronting surfaces of the parts 35 and 36 form and bound a charging duct 46 which extends longitudinally of the head. The marking medium is injected into the right hand end of this duct through action o an air jet or tube 42 which is supplied with air from a suitable soiu'ce of supply at substantially constant pressure. The air from the nozzle 42 is directed through an opening 43 into a droplet chamber 4 formed in the head 2l between parts 35 and 35; and in passing through the opening 43 suol-:s the ink or other marking medium up through the tube 45 from an ink supply reservoir 4d.

The so-called droplet chamber llfl is relatively large and the ink sprayed therein is in the form of a iine mist. Since the droplet chamber is relatively large, the atomized particles will lose most of their high blast momentum and flow slowly through the chamber 44 as a line suspension of mist. The left hand sides of the droplet chamber 44 converge gradually to the entrance to the duct 40 so that the marking liquid in the form of a mist acquires considerable velocity as it approaches the duct 4Q. On the way to the mouth of duct 40, the fast moving stream of mist is charged by ions discharged from a corona electrode. All this is similar to the construction of my prior applications above mentioned.

In the recording heads of these prior applications, however, there is but one corona electrode; and the mist particles receive but one charge in passing through the charging duct. One feature of the improved apparatus of the present invention is the provision of a plurality of corona electrodes so that repeated and successive ionic charges are applied to the stream of the marking medium and to the marking particles therein carried.

By passing the mist stream by several corona electrodes successively it has been found that the undesirable eddying and turbulence created by the charging effect of one electrode can largely, if not entirely, be obviated. The ion current of each electrode can be kept at a relatively low harmless value. Hence, in passing from one corona discharge region to the next the mild eddying, that may be present, dies down somewhat so that the mist in approaching an ionic held created by a corona electrode is relatively free from eddying and turbulence.r

In the embodiment of the invention illustrated in Figs. 3 and 4 there are three corona electrodes employed. Each corona electrode is in its own individual corona box or chamber segregated from the next corona electrode by a partition so that it will be impossible for mist tc ilow into one chamber' and out the next. The several corona chambe-s are designated 5S, and S2, respectively.

As already stated, it has been found that when a recording gun is in operation, stray mist particles sometimes accumulate on the corona rod or electrode causing an erratic corona discharge. I have overcome this by using corona wires which can be shifted to expose diierent parts of them for use sc that the part of the wire, which is active at any time, may be kept clean. In the embodiment shown, there are three corona wires 55 each of which has its opposite ends attached to pulleys 56 and 5l, respectively, which `are secured to shafts 58 and 59, respectively. -These shafts are journaled in housings 6G and'l, Yrespectively, that are secured to opposite sides of the recording head 2l.

` The current is supplied to the coronawires 55 from a suitable source through'the wire 55 which is secured to a clip S1 that has contact with one end of the shaft 58. This clip issecured to housing' by a screw 66. Pulleys 56 and 51 and shafts y58 and 59 are made of electricallyconductive metal while the housings 60 and 6| maybe made of a suitable insulating material such as plastic-or ceramic. The shafts 58 and 59 are driven by separate motors 62 and 63.

The corona chambers 50, 5I and 52 have openings or mouths 41, 48 and 49, respectively, through which the ions are discharged into the mist stream. By lpulling the corona wires 55 at a slow rate through the corona chambers, the portions of ythe wires opposite the openings 41, 48k and 49 may be continuously changed. Thus, clean, fresh portions of the wires may be continuously exposed so that the corona discharge will always be smooth.

The motors 62 and 63 are intended to operate alternately. Each is geared down to rotate at a very slow speed. The motor 62 is connected through an insulating connector 64 to the shaft 58. It drives the three pulleys 56 to cause these pulleys to wind up the corona wires 55 from the three pulleys 51. After the wires are completely transferred from one set of pulleys to the other, the motor 62 is stopped, and the motor 63 on the other shaft is set into operation to rewind the wires on the pulleys 51 on that shaft. During this operation the power to the motor E2 is shut o.

As the corona wires are wound from one set of pulleys to the other, they are preferably passed through packing chambers 68 formed in the housings 60 and El at opposite sides of the casting 35. 'These chambers 68 are iilled with packings soaked in a solvent. These packings serve both to clean the wires and to seal the charging chambers against air leakage.

At the opposite side of the duct 40 opposite each of the openings 41, 48 and 43 of the corona chambers 50, 5l, 52 is an attracting electrode 10. These attracting electrodes are mounted in the insulated lower portion 36 of the charging chamber. The voltage of the corona wire may be approximately 6,000 volts and its diameter about .005 inch. The attracting electrodes may have a negative voltage of say minus 4,000 volts. When the mist passing through the charging duct 40 passes under the corona wires, the particles of the mist are charged by ions flowing from the wires to the opposite attracting electrodes.

The ion-attracting electrodes at minus 4,000 volts not only pull down the ions but unfortunately to asmall degree displace the charged ink particles downwardly. This is ordinarily not serious unless there are very many charging sections. Then the effect becomes cumulative and a rather large number of particles will actually be precipitated on the bottom side of the charging duct 40. To prevent this I have provided repelling electrodes 15 between successive attracting electrodes. These repelling electrodes may have av positive voltage of say plus 2,000 volts. The voltage and longitudinal dimension of each re pelling electrode 13 should be such that the up- Ward thrust of each repelling electrode just balances out the downward thrust of each attracting electrode. These repelling electrodes may be silvered or inlaid areas on blocks of plastic or porous ceramic, or may be metal plates mounted directly in the insulation portion 36 of the charging chamber.

For more completely balancing out the ionic thrusts, grounded conducting plates '11 and 19 may be mounted in the lower portion 36 of the charging chamber at the entrance `'and exit ends, respectively, of duct 40. These plates are grounded by wires 11 and 18', respectively. These plates serve to pick up stray currents from the repelling electrodes. i

One advantage of using several charging sections is that each of these may be made, as already indicated, a mild charging section. The plurality of mild charging sections have a distinct advantage over a single strong charging section. The loss of marking particles by direct precipitation in the charging unit is much less When several charging sections are employed. Another advantage of multiple charging sections is that if one corona wire is not functioning properly and not discharging its full quota of ions, the other corona wires will to a considerable degree average out the charging deficiency and the record sheet 22 will still be acceptable.

As pointed out, in my application Serial No. 17,773 above mentioned, the ionic charging of the particles must take place in a strong electric field if heavy charging is to occur. Therefore, in a multiple charging unit where the final charge is acquired in the final stage, only this iinal charge need have a very high charging eld. To achieve this, the voltages on the ion-attracting electrodes in the iirst two stages can be somewhat smaller than onthe third, or the widths Aof the slot openings 41 and 48 ofthe corona chambers 50 and 5I in the first two stages can be made somewhat larger than the width of the opening 49 of the corona chamber 52 in the third stage to allow a larger number of the low velocity ions to flow into the mist stream. The turbulence will not be any greater with these wider slots because the reduced attracting electrode voltage does not impart to the ions as great an energy as in the final stage. y

Thus, in a multiple charging unit the attracting electrode voltage should progressively increase with increasing number of sections and the ionic current should preferably decrease, with increasing number of sections. This ionic current can be controlled either by altering the width of the slot openings, or the spacing of the corona wires above the slots or the mist stream, or by altering the voltage so that successive corona wires receive successively increasing voltages.

From the charging duct 40, the mist passes through a duct 34 between the precipitation plates or blocks B0 and 8| of the precipitating unit. These blocks may be made as described in my applications above mentioned. They may be made from a porous conducting material, such as powdered metal. They are separated vertically by insulating sheets (not shown) and they are separated from the charging chamber by other insulating sheets 85, They may be provided with holes, as described in application Serial No. 2,624 so that ink particles deposited on their opposed surfaces may be drawn off by suction. The insulating sheets, which separate the blocks 80 and 8! vertically, as shown in dotted lines at 82 in Fig. 4 may be shaped to converge toward each other at the left hand end of the precipitating unit to form a narrow discharge port or orice at the mouth of duct 84 through which the air or other gas with or without ink particles issues in the form of a fine stream.

The lower plate 8l may be kept at or near ground potential while the upper plate 80 has voltage signals applied thereto. rl'hese voltage signals may be applied and controlled as described in my prior applications above mentioned. When the signal is the same as the potential on the lower plate, the marking droplets in the passageway S4 between blocks 8B and Si pass therethrough in full strength with little loss in numbers by contact with the confining walls. Accordingly the ink droplets issuing from the precipitating orice will strike the record receiving sheet 22 to produce a mark thereupon. If a potential signal is applied to the upper plate S, which is dierent from the potential on the lower plate 8 I, an electric neld will be created between the upper and lower plates, and the ink or other marking particles will be drawn downward and deposited on block S I.

The percentage of particles, which are deflected or drawn downward suiciently to reach the lower plate 8l and be precipitated thereon, is determined by the magnitude of the signal. With the number of droplets precipitated on the lower plate a function of the strength of the signals applied to the upper plate, the amount of ink or other marking material deposited on the record receiving sheet 22 can be controlled. The signals as already stated, may be generated by scanning the subject matter object and may be carried by w"es 8E and 8'.' (Figs. l and 3). Before being applied to the upper plate 80, the signal current may rst pass through an amplifier 88 which serves to amplify the signals received from the signal transmitting or signal generating source.

Instead of using for the corona a length of wire wound about two pulleys, obviously, if a relatively short length wire is used and the two ends are welded together, the wire can be run continuously in one direction. This has the disadvantage, however, oi requiring a weld that may cause an erratic corona discharge when the welded portion is in the corona chamber.

Another alternativeconstruction is shown in Fig. 5. Here, instead or" using a wire, a small metallic conducting wheel 9i) having a narrow edg is used as the corona electrode. This wheel is mounted to be driven at very low speed by a motor SI. The corona wheel 90 should be suitably insulated from the motor mechanism so that it may be supplied with the corona voltage through a contact member such as contact member 92. rEhe wheel is adapted to rotate in a chamber 9d formed in the upper portion 95 of the recording head Gil. Above the chamber 94 and communicating there with may be a second chamber 9T which is filled with a suitable packing, such as glass-wool soaked in solvent. As the wheel rotates then it will be kept clean. The advantage of the wheel over the wire is that the wheel being completely rigid and with a continuously smooth corona edge can be run continuously. Also, the wheel assembly occupies less space than the wire assembly.

Otherwise, the recording head 96 might be similar in structure to the head L i.

Preferably, however, both the upper and lower portions of the charging chamber of the recording head are made of an insulating material. This may be a porous ceramic or a porous plastic, or any other suitable insulating material. Porosity is employed here, as in the previously described embodiment of the invention and asin my earlier application mentioned, to permit drawing oi by suction any marking liquid deposited on the walls of the charging duct. Holes (not shown) may be provided in the upper and lower portions of the charging chamber for conducting away the deposited liquid if desired as disclosed in my earlier applications mentioned.

Another feature of the recording head of Fig. 5 is the provision of a mixing chamber ahead of the precipitating duct to provide a more homogeneous mist for delivery to the precipitating unit.

The marking liquid may be atomized in the same way as in the recording head of Figs. 3 and e; and the atomized mist is delivered into a dispersing chamber 44, as in Figs. 3 and 4, and from there into the charging duct IIJ. The charging duct Il carries the mist stream past the opening 93 in the corona chamber 94. The opening 99 is bounded by two metallic plates 98 and opposite it is an attracting electrode IUI which is negatively charged. The duct |00 is enlarged adjacent the precipitating plates 80, 8I to provide a mixing chamber IilZ. If the charging of the particles is not smooth; if, for instance, one small volume of mist differs slightly in its properties from the neighboring volume, then the mixing or diiusing chamber IBB will aid in making up these various volumes to produce a homogeneous mist. rl'his is because in the chamber I 02 the speed of movement of the mist is slowed down and one unit of volume catches up and mixes with the preceding and succeeding units of volume.

Obviously, a plurality of corona wheels may be used along charging duct |00, just as a plurality of corona wires 55 may be used along charging duct 4Q, and for the same reason. Only one charging wheel has been shown in Fig. 5 for convenience in illustration.

Another embodiment of the invention is illustrated in Fig. 6. Here, a diiierent system is employed for preventing deposit of the marking particles on the walls of the charging duct. Here, instead of using repelling electrodes, corona chambers are provided bothA above and below the duct III] in the recording head III. The upper corona chambers are denoted at II2 and the lower chambers IIS. The openings IIS from the upper ccrona chambers are staggered with reference to the openings Ill from the lower corona chambers, so that the mist is rst charged from a lower chamber with a charge in one direction and then charged from the upper chamber with a charge in the opposite direction and these difierently directed charges alternate. This will prevent precipitation of the ink particles on the walls of the charging duct I I9. Here, the corona electrodes are shown as wires I I4 moving between spools as in the iirst described embodiment of my invention, shown in Fig. 4.

In the embodiment shown in Fig. 6, both the corona chamber openings II6 and the corona chamber openings I I7 decrease in width from the entering to the leaving end of the charging duct for the purpose explained with reference to the openings 47, 48 and B9 in the embodiment of recording head shown in Figs, 3 and 4.

Another embodiment of the invention is disclosed in Fig. 8. The corona wire can be placed very close to the slot or opening, which connects the corona chamber with the charging duct, or can be placed even inside the opening if the corona wire voltage is brought down approximately to the voltage of the slot. Then practically all the ions from the corona discharge will ilow to the opposite attracting electrode. To maintain the corona discharge, in such case, the voltage of the attracting electrode should be lowered from a negative voltage of say minus 4,000 volts to a negative voltage of say minus 8,000 volts. l

With the corona Wire placed inside of the slot, the corona chamber can be reduced in size or even eliminated, as is disclosed in the embodiment of the invention shown in Fig. 8. Here the corona wire |24 is stretched inside the recess |22 in the charging duct |20. Preferably the wire |24 is above the direct line of iiow of the mist so as not to become unduly contaminated with the mist particles.

In the recording head of Fig. 8 both the upper part |26 and the lower part |21 of the charging section are made of porous conducting metal. The portion |25 of the lower part |21 which is opposite recess |22 is insulated from the rest of the lower part |21 of the charging section and either grounded or given a negative charge. This portion |21 constitutes an attracting electrode.

There are several advantages to the corona system of Fig. 8. With the corona Wires so close to the mist stream, the charging rfield across the mist stream between the wire and the ion attracting electrode is very high. Moreover, the ionic current through the mist stream can be made very high without causing excessive electric wind disturbance. The electric wind distrubance is roughly proportional to the distance between the ion-producing and the ion-receiving electrodes. With the corona wire in a recess, such as |22, this distance can be kept small.y Another advantage is that with a small corona chamber there is less tendency for the air or mist to enter or leave the corona chamber because of the very rapid equalization of pressure inside and outside the small corona chamber or recess.

To permit the use of mists of an electrically conducting nature, such as alcohol sprays, the'insulating members must be protected from the alcohol. Figs. 8 and 9 show one way in which this may be accomplished. The ion-receiving electrode |25 is here insulated from the lower part |21 of the recording head by an insulating guard |30 which completely surrounds the electrode |25. Here the insulating guard has a porous interior. It may be made of two parts |3| and |3| which are grooved on their confronting faces to provide grooves |32 down the center of the insulation. A non-conducting iiuid, such as kerosene, may then slowly be forced constantly from a high pressure tank |33 up through the insulator. Upon einer.,- ing from the top the kerosene spreads out and is absorbed by the porous conductors |21 on either side of the electrode |25. The constant flow of the kerosene or other solvent over the top surface of the insulation maintains said top surface free of nlm of conducting alcohol or other electrically conducting marking fluid. Thus the apparatus will eifectively function with conducting marking iiuids.

Preferably the top of the insulation is set below the duct |20 providing a recess |34 above the top of the insulation. This is to keep the insulation out of the direct path of the flowing marking mist.

Obviously, this type of self cleaning insulator may be used both around the corona electrodes andA around the precipitatingl electrodes.

To clean the sides of the charging ducts, such as duct |20, and to remove therefrom any marking particles that may be deposited thereon, cleaning sprays of non-conducting iiuids, like oil or conducting solvents like alcohol can be introduced periodically into the system. It is 'especially desirable to clean the charging duct periodically if the marking fluid used isasuspension of fine marking particles in a vehicle rather than a true solution. After a few hours of operation these ne particles will begin to clog the porous Walls of the duct |20 and destroy their capillary function. For the purpose of supplying the solvent, a duct 35 may be provided in the recording head leading from a suitable source of solvent supply to the duct |20. This duct |35 is normally closed by a manually operable valve |36. Since suitable solvents are usuallyk of a conducting nature, like alcohol, it is necessary after the solvent has been turned off to supply non-conducting oil to spray and wash away the conducting alcohol from the head. The nonconducting oil spray may be supplied through a duct |31 and be controlled by a manually op erable valve |38.

The system may be shut down periodically and the solventr valve opened to supply the solvent which will dissolve the marking particles and wash them away. After the solvent valve is turned off, then the valve |38 is opened to permit the non-conducting oil to flow over the sides of the duct |20 and wash away the conducting alcohol from the system.

Obviously, the apparatus for cleaning shown in Fig. 8 can be used in any of the disclosed embodiments of the invention.

In the embodiment of the invention shown in Fig. 4 the corona wires 55 are drawn through chambers 68 iilled with packings soaked with solvent. Another way of keeping the corona wires clean is shown in Fig. 'l'. Here a tube or tubes |40 are mounted in Walls of the one or both of the spool housings 60 and 6|; and tubular swabs |4| are mounted in these tubes around the corona wires. The swabs may be pushed in and out of the corona chambers along the corona wires manually or automatically, to clean the corona wires. Clean corona wires are essential to avoid uneven corona discharge.

An alternate arrangement for keeping thecorona wires clean is shown in Fig. l0. Here a tank or reservoir |41 iilled with a solvent is connected by main duct |48 and branch ducts |45 with the several corona chambersv50, 5| and 52. Flow of the solvent to the corona chambers is controlled by the valves |43. l To clean the wires, the valves |49 are opened periodically so that solvent may be squirted or sprayed from the reservoir on the wires.

As shown in Figs. 3, 6 and 10, the corona chambers may be covered ywith a cover plate |50 made of an insulating material such as plastic or ceramic. This will conne the corona discharge to the recording head. To insure the maximum eiciency of the corona discharge the corona chamber 50, 5|, 52 (Fig. 1), 94 (Fig. 5), ||2 and ||3 (Fig. `6), and |22 (Fig. 8) may be coated inside with insulation, or a second shielding electrode may be placed above each corona electrode, which is of the same potential as the corona electrode, and which will prevent the ions from the corona electrode from dissipating themselves on the upper walls of the corona chamber and cause these ions to be directed at the mist stream.

In all of the embodiments of the invention it is preferred to widen the charging duct or channel laterally opposite each of the corona chamber openings. The lateral recesses so formed are de-l noted at 53, 5 and 53 in Fig. 4 and |23 in Fig. 9. The recess permits full charging of the mist particles flowing very closely to the channel wall.

Without the recess these particles would not be fully charged because of the weakening of the charging electric field in the immediate vicinity of the side wall of the channel or duct due to the side wall. With the side wall recessed the disturbing inuence of the wall is removed. The mist stream flows essentially in a straight line past the recess with but only partial flow into the recess. The small portion of the stream that does penetrate into the recess is moving at reduced speed and so is extra heavily charged.

The long recesses I52 (Fig. 4) at the junction between the corona wire and the supporting insulation are intended to provide partial protection against spray mist particles falling on said junctions. As the reels or spools 56 and 51 revolve; and the corona wires are drawn away from said junctions, it is desirable that the clean wires do not drag away with them the ink deposits from said junctions. If necessary, clean air may be slowly introduced into the recesses, as in the case of my application Serial No. 2,624 to keep out any mist vapors. This clean air has another purpose also, namely, to maintain a slight positive pressure in each corona chamber that tends to keep stray mist particles from entering the corona chamber through the slot openings 47, 48 and 119.

While the invention has been described in connection with several diferent embodiments thereof, it is capable of further modincation, and this application is intended to cover any variations, uses, or adaptations of the invention iollowing, in general, the principles of the invention and including such departures from the present disclosure as come within known o1' customary practice in the art to which the invention pertains and as may be applied to the essential features hereinbefore set forth and as fall within the scope of the invention or the limits of the appended claims.

Having thus described my invention, what I claim is:

l. A recording head of the character described comprising means for entraining marking particles in a gas, a duct through which a stream containing the entrained marking particles may be passed, a corona electrode, whose discharge portion has linear extent, mounted in said head in operative position, at one side of said duct, to charge the particles in said stream, means for moving said electrode in the head to bring different areas of its discharge portion successively into charging position, a precipitating unit having a passageway therethrough communicating with said duct and into which the charged particles pass, and means for creating an electrical field in said passageway, the intensity of which is controlled in accordance with received signals.

2. A recording head of the character described comprising means for entraining marking particles in a gas, a duct through which a stream containing the entrained marking particles may be passed, a corona wire movably mounted in said head, means for moving the wire linearly to bring different parts of it into operative relation to the duct to charge the particles in the stream, a precipitating unit having a passageway therethrough into which the charged particles pass and means for creating an electrical iield in said passageway, the intensity of which is controlled in accordance with received signals.

3. A recording head of the character described comprising means for entraining marking particles in a gas, a duct through which a stream containing the entrained marking particles may be passed, a pair of spools journalled in said head, a corona wire mounted to be wound from one spool onto the other, means for rotating the spools so that different parts of the Wire are brought successively into operative relation with said duct to charge the particles in said stream, a precipitating unit having a passageway therethrough into which the charged particles may pass, and means for creating an electrical eld in said passageway, the intensity of which is controlled in accordance with received signals.

4. A recording head of the character described comprising means for entraining marking particles in a gas, a duct through which a stream containing the entrained marking particles may be passed, a corona electrode whose discharge portion has linear extent mounted in said head in operative position at one side of said duct to charge the particles in said stream, said corona electrode comprising an endless corona wire, means for moving said wire so that different parts of it are brought successively into operative relation with said duct to charge the particles in said stream, a precipitating unit having a passageway therethrough communicating with said duct into which the charged particles may pass, and means for creating an electrical eld in said passageway, the intensity of which is controlled in accordance with received signals.

5. A recording head of the character described having a duct extending therethrough through which a stream containing marking particles entrained in a gas may be passed, a corona electrode whose discharge portion has linear extent, mounted in said head in operative relation to said duct to charge the particles in said stream, means for moving the electrode in the head to bring different areas of its discharge portion successively into charging position, means for cleaning said electrode, a precipitating unit having a passageway therethrough into which the charged particles pass from the duct, and means for creating an electrical field in said passageway, the intensity or" which is controlled in accordance with received signals.

6. A recording head of the character described having a duct extending therethrough through which a stream containing marking particles entrained in a gas may be passed, a corona electrode, whose discharge portion has linear extent, mounted in said head in operative relation to said duct to charge the particles in said stream, means for moving the electrode in the head to bring different areas of its discharge portion successively into charging position, a packing chamber having cleaning means therein through which the corona electrode travels in its movement, a precipitating unit having a passageway therethrough into which the charged particles pass from the duct, and means for creating an electrical eld in said passageway, the intensity of which is controlled in accordance with received signals.

'7. A recording head of the character described comprising means for entraining marking particles in a gas, a duct through which a stream containing the entrained marking particles may be passed, a corona electrode whose discharge portion has linear extent mounted in said head in operative position at one side of said duct to charge the particles in said stream, said corona electrode comprising a charging corona wheel rotatably mounted in said head, means for rotating the wheel to bring different parts of its periphery into operative relation to said duct to charge the particles in the stream, a precipitating unit having a passageway therethrough communicating with said duct into which the charged particles may pass from the duct, and means for creating an electrical eld in said passageway, the intensity of which is controlled in accordance with received signals.

8. A recording head of the character described comprising means for entraining marking particles in a gas, a duct through which a stream containing the entrained marking particles may be passed, a corona electrode whose discharge portion has linear extent mounted in said head in operative position at one side of said duct to charge the particles in said stream, said corona electrode comprising a charging corona wheel rotatably mounted in said head, means for rotating said wheel to bring different parts of its periphery into operative relation to said duct to charge the particles in the stream, a cleaning chamber through which said wheel passes in its rotation, a precipitating unit having a passageway therethrough communicating with said duct into which the charged particles may pass from the duct, and means for creating an electrical field in said passageway, the intensity of which is controlled in accordance with received signals. 9. A recording head of the character described having a duct extending therethrough throughv which a stream containing marking particles entrained in a gas may be passed, a corona electrode mounted in said head in operative relation to said duct, said duct being widened laterally opposite said corona electrode, a precipitating unit having a passageway therethrough into which the charged particles may pass from said duct, and means for creating an electrical eld in said passageway, the intensity of which is controlled in accordance with received signals.

10. A recording head of the character described having a duct extending therethrough through which a stream containing marking particles entrained in a gas may be passed, a plurality of corona electrodes mounted in operative relation to and spaced along said stream to impart successive ionic charges thereto, a precipitating unit having a passageway therethrough into which the stream may pass from said duct and means for creating an electrical eld in said passage- Way, the intensity of which is controlled in accordance with received signals.

11. A recording head of the character described having a duct extending therethrough through which a stream containing marking particles entrained in a gas may be passed, a plurality of corona electrodes mounted in operative relation to and spaced along said stream to create successive ionic charging atmospheres through which the stream passes and the held-strength of which is greater in the latter stages than in the first stage, a precipitating unit having a passageway therethrough into 'which the stream may pass from said duct, and means for creating an electrical field in said passageway, the intensity of which is controlled in accordance with received signals.

12. A recording head of the character scribed having a duct extending therethrough through which a stream containing marking particles entrained in a gas may be passed, a plurality of corona electrodes mounted in operative relation to and spaced along said stream to create successive charging atmospheres through which said stream passes and the held-strength of which increases progressively, a precipitating unit having a passageway therethrough into which the stream may pass from said duct, and means for creating an electrical eld in said passageway, the intensity of which is controlled in accordance with received signals.

13. A recording head of the character described having a duct extending therethrough through which a mist stream containing marking particles entrained in a gas may be passed, a plurality of corona electrodes mounted in the head at one side of said duct in operative relation thereto and spaced from one another in the direction of flow of said stream, ion-attracting electrodes mounted in the head at the opposite side of said duct and insulated from one another,

and means for balancing the thrusts of the attracting electrodes to prevent precipitation of droplets of mist on the walls of the duct, a precipitating unit having a passageway therethrough into which the stream may pass from said duct, and means for creating an electrical field in said passageway, the intensity of which is controlled in accordance with received signals.

14. A recording head of the character described comprising means for entraining marking particles in a gas, a duct through which a stream containing the entrained marking particles may be passed, a plurality of corona electrodes mounted inl said head in operative relation to and spaced along said stream tocharge the particles in said stream, said electrodes being each of linear extent and being so disposed relative to said stream that their charging thrusts balance, means for moving each of said electrodes in the head to bring different areas of its discharge portion successively into charging position, a precipitating unit having a passageway therethrough communicating with said duct and into which the stream may pass from said duct, and means for creating an electrical eld in said passageway, the intensity of which is controlled in accordance with received signals.

l5. A recording head of the character described comprising means for entraining marking particles in a gas, a duct through which a stream containing the entrained marking particles may be passed, a plurality of corona electrodes mounted in the head at one side of said duct in operative relation thereto and spaced from one another in the direction of flow of said stream, a plurality of corona electrodes mounted in the head at the opposite side of the said duct in operative relation thereto and alternating with the first-named electrodes along the direction of flow of said stream, each of said electrodes having a discharge portion of linear extent, means for moving each electrode in the head to bring different areas of its discharge portion successively into charging position, a precipitating unit having a passageway therethrough communicating with said duct and into which the streamvmay pass from said duct, and means for creating an electrical field in said passageway, the intensity of which is controlled in accordance with received signals.

16. A recording head of the character described having' a duct extending therethrough through which a stream containing marking particles entrained in a gas may be passed, a plurality of corona electrodes mounted in the head at one side of said duct in operative relation thereto and spaced from one another in the direction of now of said stream, an ion-attracting electrode mounted in one wall of said duct opposite each of the corona electrodes, and repelling electrodes mounted in said one wall or" the duct between successive ion-attracting electrodes, the voltage and longitudinal dimension of each repelling electrode being such as to offset the thrust on the stream of theattracting electrodes, a precipitating unit having a passageway therethrough into which the stream may pass from said duct, and means for creating an electrical iield in said passageway the intensity of which is controlled in accordance with received signals.

17. A recording head of the character described having a duct extending therethrough through which a stream containing marking particles entrained in a gas may be passed, a plurality of corona chambers provided in said head at one side of said duct and spaced from one another in the direction of flow of said stream, a charging corona electrode mounted in each of said chambers, a slot-opening in the head leading from each of said chambers into the duct to permit discharge of ions from the corona electrodes into the stream, an ion-attracting electrode mounted in one wall of the duct opposite each of said openings, some of said slot-openings being narrower than others, the ion-attracting Yelectrodes which are opposite the wider slots having lower voltages than those opposite the narrower slots, a precipitating unit having a passageway therethrough into which the stream may pass from said duct, and means for creating an electrical neld in said passageway, the intensity of which is controlled in accordance with received signals.

i8. A recording head of the character described having a duct extending therethrough through which a stream containing marking particles entrained in a gas may be passed, a plurality of corona chambers provided in said head at one side of said duct and spaced from one another in the direction of flow of said stream, a corona electrode mounted in each of said chambers, a slot-opening in the head leading from each of said chambers into the duct to permit discharge of ions from the corona electrodes into the stream, the slot-openings or successive chambers being progressively narrower in width in the direction of flow of the stream, an ion-attracting electrode mounted in one wall of the duct opposite each of said openings, said ion-attracting electrodes having progressively higher voltages in the direction of stream-flow, a precipitating unit having a passageway therethrough into which the stream may pass from said duct, and means for creating an electrical eld in said passageway, the intensity of which is controlled in accordance with received signals,

i9. A recording head of the character described having a. duct extending therethrough through which a stream containing marking particles entrained in a gas may be passed, a plurality of separate corona chambers provided in said head at one side of said duct and spaced from one another in the direction of flow of said stream, an opening in the head leading from each or said chambers into the duct to permit discharge of ions from the corona electrodes into the stream, an ion-attracting electrode mounted in one wall of the duct opposite each of said openings, the several ion-attracting electrodes being insulated from one another, said duct being widened out laterally opposite each of said openings, a precipitating unit having a passageway therethrough into which the stream may pass from said duct, and means for creating an electrical eld in said passageway, the intensity of which is controlled in accordance with received signals.

20. A recording head of the character described having a duct extending therethrough through which a stream containing marking particles entrained in a gas may be passed, a corona chamber provided in said head at one side of said duct, a charging corona electrode whose discharge portion has linear extent mounted in said chamber, a slot-opening in said head leading from the corona chamber into the duct to permit discharge of ions from the corona electrode into the stream, means for moving the electrode in said head to bring different areas of its discharge lportion successively into charging position, an ion-attracting electrode mounted in one wall of the duct opposite said slot-opening, means for supplying a solvent for the marking particles to said corona chamber to clean said charging electrode, a precipitating unit having a passageway therethrough into which the stream of charged particles may pass from said duct, and means for creating an electrical field in said passageway, the intensity of which is controlled in accordance with received signals,

21. A recording head of the character described comprising means or entraining marking particles in a gas, a duct through which a stream containing the entrained marking particles may be passed, a charging corona electrode mounted in said head at one side of said duct in operative relation thereto, to charge the particles in said stream, said charging electrode having a discharge portion of linear extent, means for moving said electrode in said head to bring different areas of its discharge portion successively into charging position, an ion-attracting electrode mounted in the head opposite said corona electrode, an insulator surrounding said attracting electrode, said insulator being porous, and the wall of the duct in which the attracting electrode and the insulator are mounted being porous also, means for forcing a cleaning fluid up through the pores of the insulator into the duct, the precipitating unit having a passageway therethrough communicating with said duct and into which the stream may pass from said duct, and means for creating an electrical eld in said passageway, the intensity of which is controlled in accordance with received signals.

22. A recording head of the character described comprising means ior entraining marking particles in a gas, a duct through which a stream containingr the entrained marking particles may be passed, a charging electrode whose discharge portion has linear extent mounted in said head at one side of said duct in operative relation to the duct to charge the particles in said stream, means for moving said electrode in said head to bring different areas of its discharge portion successively into charging position, an insulator for insulating the corona electrode from the head, an ion-attracting electrode mounted in the head opposite said corona electrode, an insulator for insulating the attracting electrode from the head, a precipitating unit having a passageway therethrough communicating with said duct and into which the stream may pass from said duct, an insulator for insulating the precipitating unit from the rest of said head, means for creating an electrical eld in said passageway, the intensity of which is controlled in accordance with received signals, one, at least, of said insulators being porous, and means for 17 forcing a cleaning liquid through the pores of said insulator.

23. A recording head ofthe character described comprising means for entraining marking particles in a gas, a duct through which a stream containing the entrained marking particles may be passed, a charging corona electrode, whose discharge portion has linear extent, mounted in said head at one side of said duct in operative relation thereto to charge the particles in said stream, means for moving said electrode in said head to bring diierent areas of its discharge portion successively into charging position, an ion-attracting electrode mounted in the head opposite said corona electrode, means for supplying a cleaning solvent to said duct to remove marking particles deposited on the walls of the duct, a precipitating unit having a passageway therethrough communicating with said duct and into which the stream may pass from said duct, and means for creating an electrical field in said passageway, the intensity of which is controlled in accordance with received signais.

24. A recording head of the character described having a duct extending therethrough through which a stream containing marking particles entrained in a gas may be passed, said duct being recessed, a charging corona electrode positioned in said recess above the direct line of ow of the stream, an ion-attracting electrode mounted in the wall of the duct opposite the corona electrode, a precipitating unit having a passageway therethrough into which the stream may pass from said duct, and means for creating an electrical field in said passageway, the intensity of which is controlled in accordance with received signals.

25. A recording head of the character described comprising means for entraining marking particles in a gas, a duct through which a stream containing the entrained marking particles may be passed, a charging corona electrode, whose discharge portion has linear extent, mounted in said head at one side of said duct in operative relation thereto to charge the particles in said stream, means for moving said electrode in the head to bring different areas of its discharge portion successively into charging position, ion-attracting means in the opposite side of said duct, said duct being enlarged beyond the electrode charging area to provide a mixing chamber for the charged particles, a precipitating unit having a passageway therethrough communicating with said duct and into which the charged particles may pass from said mixing chamber, and means for creating an electrical eld in said passageway, the intensity of which is controlled in accordance with received signals.

26. A recording head of the character described having a duct extending therethrough through which a stream containing marking particles entrained in a gas may be passed, :a plurality of charging corona electrodes mounted in operative relation to said duct, an ion-attracting electrode mounted at the opposite side of the duct to each of the charging electrodes, said charging electrodes being adapted to produce ionic currents progressively decreasing in the direction of stream-flow, said attracting electrodes having attracting electrode voltages progressively increasing in the direction of streamflow, a precipitating unit having a passageway therethrough into which the stream may pass from said duct, and means for creating an electrical field in said passageway, the intensity of which is controlled in accordance with received signals.

CARLYLE W. JACOB.

REFERENCES CITED The following references are of record in the le of this patent:

UNITED STATES PATENTS Number Name Date 1,360,654 Littlefield Nov. 30, 1920 1,841,452 Ranger Jan. 19, 1932 1,941,001 Hansell Dec. 26, 1933 2,172,539 Kimmich Sept. 12, 1939 2,302,289 Bramston-Cook Nov. 17, 1942 

